Uneven distribution of the particulate content in paint can cause mottling, also known as striping, banding, shadowing, flooding, floating, misting, precipitation, blooming, bloom, or bleaching. Mottling typically occurs in metallic paints, when the flakes float together to produce a spotty or striped appearance in a coating resulting from such a paint. The foregoing defect can be minimized by adjusting the rheology of the paint such that aggregation or settling of flakes and/or pigments in the paint is minimized. Typically, rheology additives, such as BYK®-411 rheology additive supplied by BYK USA Inc. of Wallingford, Conn. are well suited for this purpose. Such rheology additives are added during the manufacture of the paint to control the in-can and application viscosities of the paint. However, if too much of these rheology additives are added, then coating defects, such as fish eye, cratering or orange peel appearance can result. If too little of these rheology additives are added, then the aforedescribed mottling defect can occur. Thus, it is critical for the paint manufacturer to be able to predict the degree of mottling that can result in paint being manufactured.
Typically during the manufacturing of coating compositions, such as flake containing automotive OEM or refinish paints, from time to time, an aliquot of such coating compositions being manufactured is taken, applied as a layer of desired thickness over a test substrate, dried and/or cured into a coating and its degree of mottling acceptability is assessed visually. The flop is defined in ASTM E284. The process parameters are then adjusted and the aforedescribed testing procedure is repeated until the adjusted coating composition meets the desired degree of mottling.
The aforementioned testing procedure is not only time consuming and cumbersome but it also results in frequent interruptions in the manufacturing process. As a result, the batch-to-batch quality of the resulting coating compositions can be detrimentally affected. Therefore, a need exists to develop a process that could predict the degree of mottling in a coating that would result from a coating composition while it is still being manufactured such that the manufacturing process could be readily adjusted on a real time basis to attain the desired degree of mottling.